Chapter 2. Perception

Question 1

Perception is…

Answer 1

the subjective experience of sensory information after having been processed by the cognitive processes (e.g. attention). As compared to “sensation”
The information comes in from the senses (sensation) and then this information is processed in different steps. The end result is perception

Question 2

How does visual perception work in general terms?

Answer 2

The light is reflected from objects and reaches the eye. From the light that reaches our visual system we extract information about objects and the environment around us to be able to optimally interact. We sort of reconstruct the surroundings in our brain from the information received and that reconstruction is our perception

Question 3

Optical elements (lenses) of the eye are :

Answer 3

• cornea
• lens

Question 4

What is a retina? What does it receive?

Answer 4

light-sensitive array at the back of the eye. Receives the waves of light. receives an inverted image (however post-processing copes with it easily)

Question 5

The 3 steps of visual perception:

Answer 5

• Reception: absorption of physical energy
• Transduction: physical energy is converted into an electrochemical pattern in the neurons
• Coding: each neuron activating the next one and so-on; one-to-one correspondence between aspects of the physical stimulus and aspects of the resultant nervous system activity

Question 6

What imaging modes do eyes have?

Answer 6

• Night vision (low light)
• Daylight vision (high intensity)

Question 7

What are rods?

Answer 7

Rods are photoreceptors active only in low light. Rods are very sensitive, able to detect the lowest amounts of light. In bright light they stop functioning.

Question 8

What are cones and what types are they?

Answer 8

Cones are photoreceptors active in daylight. They are divided in three types, maximally sensitive to different wavelengths of light that we label red, green and blue. Cones only activate when there’s enough light and are less sensitive

Question 9

What do “opponent” color channels do?

Answer 9

They help enable the differentiation between different wavelengths
Cones feed into two opponent color channels: one can signal blue or yellow, the other red or green. They are processing and comparing different wavelengths

Question 10

Can humans distinguish color at low light levels? why?

Answer 10

No, because only rods are active in low light

Question 11

What is the Purkinje effect?

Answer 11

The tendency of color sensitivity to shift from red to blue at low light levels
In high light levels eyes are more sensitive to green/yellow bc of cones; in low light eyes have higher green/blue sensitivity bc of rods.
This change is the Purkinje effect

Question 12

Key characteristics of Gibson’s view on perception

Answer 12

• Not important how perception works, but what it is for
• Perception should be considered in terms of how it allows up to interact with the world we live in
• Perception is direct: sensory information contained within the stimulus is so rich that it allows a person to move around and interact with the environment without the need for any top-down processing
• Gibson denies the use of stored knowledge
• Some aspects of the world are invariant, and we have evolved to exploit those invariants

Question 13

What is direct perception according to Gibson?

Answer 13

Perception that is based on the input, without the need for top-down processing

Question 14

Explain structural invariants

Answer 14

if light from a particular direction falls on an object of a particular shape and surface texture, the shadows and shading around that object will always be the same

Question 15

Explain transformational invariants

Answer 15

as we move through the world, the image of the world we perceive will flow past us (“optic flow”). The basic nature of that flow and the way it changes is invariant

Question 16

What does “optic flow” help people with?

Answer 16

Perceiving optic flow allows us to judge how fast we are moving, and helps us avoid running into things

Question 17

What is the problem with Gibson’s theory?

Answer 17

It is too extreme. While there is evidence that some parts of the perceptual process works in a “Gibsonian” way, the key phrase still is “some parts” and not “all parts”. Most things are not explained by the Gibsonian approach

Question 18

What is the evidence of some parts of perceptual process working in a “Gibsonian” manner?

Answer 18

• affordances are coded automatically: if you show a person a hammer, brain activity in the region for grasping a tool in a certain way is automatically activated
  -direct perception would make sense when we need to do some kind of task very fast